A defogging device defogging a windshield of a vehicle is known to have a humidity sensor that detects humidity near a surface of the windshield. The defogging device performs a defogging control, in which a conditioned air is blown toward the surface from a defroster outlet to defog the windshield, depending on a detection value of the humidity sensor. Such a technique is described in Patent Literature 1, for example.
The defogging device has a temperature sensor, a memory, and a control unit. The temperature sensor detects a temperature around the humidity sensor. The memory stores, as a function, relationship between the temperature around the humidity sensor and a response delay time of the humidity sensor in advance. The control unit calculates the response delay time of the humidity sensor based on a detection value of the temperature sensor.
The control unit compensates for the response delay of the humidity sensor based on a calculated response delay time and a change rate of an output from the humidity sensor, and then performs the defogging control depending on the detection value of the humidity sensor being compensated for the response delay.
Thus, the response delay of the humidity sensor caused by the temperature around the humidity sensor is compensated for by use of the detection value of the temperature sensor. As a result, it is possible to improve detection accuracy of the humidity sensor.